You can send a file as an attachment using several different digital modes. It works just like sending an email with an attached file. Pactor using Winlink is popular with yachtsmen; in the (US) ham bands you are (legally) limited to Pactor I, with a relatively low baud rate, but the US military's MARS system uses up to Pactor III.PACTOR - Wikipedia, the free encyclopedia

Short distances via V/UHF is not much of a problem...or via linked repeaters. Long range, via HF is very problematic since the bandwidth is pretty small, which is why hams did SSTV - one frame every minute or so. Regular TV has a bandwidth of 6Mhz and transmits 30 frames per second, SSTV via HF is 3KHz....

Now, using various forms of encryption you can put a lot into a single frame of a picture... cf. Steganography.

Do I treat Glocks like I treat my lawn mowers? No, I treat them worse. I treat my defensive weapons like my fire extinguishers and smoke detector - annual maintenance and I expect them to work when needed

As others have mentioned the data could be sent using some version of Packet Radio, but it would not be real time.

However real-time transmission of video is quite possible on the ham bands, particularly in the UHF spectrum where the needed bandwidth is available. The cheap way to do this is to use video modulators designed for cable TV systems. If you choose the right cable TV channel you will be in the middle of the 70 cm ham band. Most ham TV is done using the old analog transmission method since the range is so much better than using the more modern digital TV that over the air commercial broadcasting has switched to. For greater range it is quite possible to use repeaters that are made for this purpose.

Back to the scenario again: The character created a two minute video using a pocket videocam recording to an SD chip (or something similar).

He doesn't need realtime, he doesn't need broadcast, he just needs to get that file sent back to a friend in an unaffected area beyond the Rockies who will know what to do with it. I have already established that one of the main characters is in contact with a Ham who is able to transmit by whatever means back across the Rockies.

The question is can this ham take that chip and get that file to the other end of the line?

What procedure will he likely use to do so. I'm not terribly concerned with legality here, folks, only that it works.

The question is can this ham take that chip and get that file to the other end of the line?YES.What procedure will he likely use to do so. I'm not terribly concerned with legality here, folks, only that it works.

See my post above--for High Frequency bands, best digital mode at this time is using PACTOR and Winlink/airmail, attach video file to message just like email.

Feel free to disregard my aside about baud rate allowed on ham bands, I doubt the FCC even monitors that today, let alone after a disaster. Legal out for going at a higher rate is that it makes getting the word out more sure, and "any means available in a disaster" is written into the regs.

The character created a two minute video using a pocket videocam recording to an SD chip (or something similar).

OK lets take for example my Panasonic DMC-ZS3 pocket camera which is an inexpensive video capable camera. Using Motion JPEG encoding (the easiest for someone to decode without special software) in full HD video it takes 512 MB (4,294,967,296 bits) for 2 minutes of video. Using the lowest resolution QVGA setting (320 by 240 pixels) 1 min 50 seconds of video will fit in 64 MB (536,870,912 bits) of space.

he just needs to get that file sent back to a friend in an unaffected area beyond the Rockies who will know what to do with it.

When I was talking about real time video on ham frequencies I was talking point to point line of sight transmissions.

For your application Drang is right you are talking HF bands not UHF. With the PACTOR transmission mode Drang mentioned you can get 100 to 200 baud data rates depending on how good and interference free the ham band chosen is at that moment.

Assuming 100 baud and QVGA (low) quality video, and assuming you can maintain a HF connection 24/7 (no way) instead of for a few hours a day when conditions are right (the real world), then it would take over 62 days to send that 1 min 50 second low quality video.

Think about using the LiveU set. It can used on radios or cells or sat-phones.

It is in fact the poorman's sat-truck. It is be used to replace them. A TV producer is very, very likely to know about them. They have hardware compression built-in. It has adaptive bandwidth, depending on availability.

According to the LiveU page, their system uses the cellular 3g/4g network. There is no cellular network available to my guy. And all his sat truck transmissions are being blocked by the USGOV at the satellite and not being forwarded to broadcasters.

Can a 4MB data file be transmitted from San Francisco to, say Denver, by any known HAM system in a reasonable amount of time?

According to the LiveU page, their system uses the cellular 3g/4g network. There is no cellular network available to my guy. And all his sat truck transmissions are being blocked by the USGOV at the satellite and not being forwarded to broadcasters.

Can a 4MB data file be transmitted from San Francisco to, say Denver, by any known HAM system in a reasonable amount of time?

Suburban says no, Drang is a yes, but I'm not clear on his yes.

Anybody?

No, the LiveU isn't limited to cell networks. It's primarily a Mux/DeMux unit with capabilities of up to 14 input/outputs. It has the hardware for different data compression techniques, and the video data can be fed into server, to be transmitted, or you can use the builtin FTP, to transmit it out, via packet (if the total bandwidth you can achieve is less than 4mbs.)

Understand, you'd have to arrange to have your Transceivers to transmit and recieve simultaneous different frequencies, but it can be done. (like I said, up to 14 different transceivers.)

I don't understand how the US Gov. could block Inmarsat. (BGAN, etc) Aren't they UK based, international company, with 10 of their own Sats? These are LEO sats, used primarily for Martine use. Expensive as all get out, but really usable in the field. Surely, some were protected, from the EMP.

Pactor III, while it may not be legal in the U.S., is available with units from PSC selling for 1200-1800 dollars. They offer baud rates up to 5200/s.

Now, I realize that such things aren't perfect, and I'm probably confusing myself here, but wouldn't that rate transmit a 4MB file in twelve minutes or so?

Also, I'm unclear on just how much a PACTOR III setup would compress the original 4MB file for purposes of transmission.

I don't recall what the compression rate is off the top of my head, but I do remember that it would be de-compressed on receipt. And a 12 minutes transmission time may seem grueling, but it works.

Frankly, Bill, I think this is one of those areas where you as the author shouldn't get bogged down in the details of what is technically possible, right now. There are enough experimental protocols out there that you should be able to write "attached the compressed video file to the text message, fired up his radio and Terminal Node Controller (AKA 'Radio Modem'), and sent the message to Elmer in Colorado", with maybe "via the message server in Milwaukee, which was the closest one operational" without any but the most hypercritical objecting. As a matter of personal taste, one of if not the biggest problems with Rawles' writing tends to be his tendency to describe in loving detail every single technical point in a process...

I believe that PACTOR IV is supposed to be out there, and some rival modes are doing away with the TNC.

Thanks, Drang. I'll probably go that way. Your advice is especially valuable, since the ham in question in the book is the bar pilot who several hundred pages earlier guides the Makin and the Lincoln and the rest of the CSG into the SF Bay, and who just happens to be named D.W. Drang.

Now, I realize that such things aren't perfect, and I'm probably confusing myself here, but wouldn't that rate transmit a 4MB file in twelve minutes or so?

4 MB is 33,554,432 bits (1 MB is 1,048,576 bytes, and there are 8 bits in a Byte). With a data rate of 5200 bits per second that is nearly 1.8 hours, not 12 minutes. Still all in all that is a possibly workable length of time.

So you are not just taking the SD card out of the camera and transmitting that. First, you must use video compression software to crunch the original camera file down to 4 MB. Then both ends of the link must have the PACTOR III or IV modems which are sole sourced out of Germany. They are not something the average ham will have, but it is still possible.

Also, I'm unclear on just how much a PACTOR III setup would compress the original 4MB file for purposes of transmission.

I have not investigated the data rate claims of the newer PACTOR modems, but the video compression software that produced the 4 MB file has already taken out all the redundant information in the video, so if the claimed PACTOR data rates are based on the use of data compression, then you will not get those rates because there is nothing left to compress in the 4 MB file. If the data rate claims are strictly based on a very efficient data modulation scheme, then you should get what is claimed.

And lots of blue-water boaters use PACTOR III for HF Email. I've thought about setting up a sailmail gateway with antennas pointing mostly NW or NE from the Estancia, covering arctic regions not well covered. The issue is mainly one of cost, suitable hardware would be around $50k including towers.

Do I treat Glocks like I treat my lawn mowers? No, I treat them worse. I treat my defensive weapons like my fire extinguishers and smoke detector - annual maintenance and I expect them to work when needed

So you are not just taking the SD card out of the camera and transmitting that.

This is why I sometimes have trouble understanding the advice of experts.

I said:

Quote

I just watched an 80 second mp4 file that weighed in at 5.6MB.

This file was, indeed, what was on the SD card. It is a video I made with a small handheld camera. A one minute video made with that camera would, I assume, be closer to four MB on the SD card. So that's what you would start with, before applying any compression.

Anyway, thanks for all your help. I've written the scene, and it works well. It's also vague enough (but still within the bounds of possibility) that I don't think it will mortally offend any hams who happen to read it.

This is why I sometimes have trouble understanding the advice of experts.

I said:This file was, indeed, what was on the SD card. It is a video I made with a small handheld camera. A one minute video made with that camera would, I assume, be closer to four MB on the SD card. So that's what you would start with, before applying any compression.

Correct?

I consider it a failure in my explanation when someone can't follow what I wrote, so lets see if I can make it any clearer.

Uncompressed digital video has a data rate of about 200 MB per second. Professional grade HD video cameras send the video out at this rate. Consumer grade cameras compress the video to get the data rate down to something manageable. There are two ways this is done. The first uses algorithms that search for patterns, send the pattern once and then indicate repeats in each pattern throughout the image, and from image to image in the stream of images that make up a video. The second much simpler way to compress the video is to make the image size smaller (less pixels).

My pocket camera offers two different algorithms for compressing the video. The more aggressive one is Motion JPEG, and combined with reducing the image size to 320 by 240 pixels, results in a file of about 35 MB for a one minute video. That is what my camera puts on its SD card.

There are even more aggressive video compression schemes that trade off lower quality video for reduced data rates (and therefore file sizes). If you were using a camera similar to mine, you would need to use a program on your computer that did this further video compression. Evidently the example you gave had a much more aggressive video compression algorithm built into the camera.

Yes there are algorithms that can crunch the rate down lower, but with even further trade-offs in video quality and/or image size. My video editor son just did some tests for me and found that he could get a minute of 320x240 video down to about 3.5 MB, so the file size you mention is certainly possible.

Once again, Suburban, Drang, ER, and Ken, thanks for your help. It all worked out well in the end. I'm still almost completely illiterate about ham and video compression algorithms, but at least I think I've avoided making a fool out of myself in the novel, thanks to you guys, so I've very grateful - both to you, and to the internet that makes you easily available to me for stuff like this.